This invention relates to circuits for measuring impedance and admittance and, more particularly, to a circuit for measuring the real and imaginary parts of both impedances and admittances.
The majority of prior art impedance measuring circuits utilize bridge-type networks. Such prior art arrangements measure an unknown impedance by utilizing a number of variable impedance elements to form three arms of a bridge with the fourth arm of the bridge comprising the unknown impedance. The variable impedance elements are adjusted until a null appears across the bridge, at which time the values of the ratios of the variable impedance elements determine the value of the unknown impedance.
One specific prior art arrangement disclosed in U.S. Pat. No. 3,284,705, issued to Dobson on Nov. 8, 1966, drives an unknown impedance with a fixed sinusoidal current signal. Two signals are derived from the driving current signal one in phase with the current signal, and the other having a -90 degree phase relation to the current signal. The two derived signals are used separately to gate the response voltage signal generated across the unknown impedance to two separate direct current microammeters which serve to integrate the gated signals. The signal gated by the derived inphase signal yields the real part of the unknown impedance while the signal gated by the derived phase shifted signal yields the imaginary part of the unknown impedance.
These prior art measuring circuits are bulky, expensive, and not in keeping with modern day technology. Furthermore, no known prior art measuring circuit has the capability of directly measuring the real and the imaginary parts of both the impedance and the admittance of a connected load.